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Saturday, November 14, 2015

Fermentasi

Since fruits ferment naturally, fermentation precedes human history.
However, humans began to take control of the fermentation process at some
point. There is strong evidence that people were fermenting beverages in Babylon circa 5000 BC, ancient
Egypt circa 3000
BC, pre-Hispanic Mexico circa 2000 BC, and Sudan circa 1500 BC. There
is also evidence of leavened bread in ancient
Egypt circa 1500
BC and of milk fermentation in Babylon
circa 3000 BC.
The Chinese were probably the first to develop vegetable fermentation.

Throughout human history, bacteria
and fungi have been intimately involved with both the success and failure of
daily life. Microorganisms cause disease, but they also play a wider role in
sustaining life. We know that certain bacteria play a major part in recycling
chemical elements as well as compounds. For example, bacteria help return the
materials of dead organisms back to the earth, so those materials can be used
by living organisms. What's more, without bacterial action, living things would
not be able to use certain compounds found in soil, water, and even the
atmosphere. Modified versions of these microorganisms are now essential in
modern day pharmaceutical production.

In fermentation, microorganisms such as bacteria, yeasts, and molds
are mixed with ingredients that provide them with food. As they digest this
food, the organisms produce two critical by-products, carbon dioxide gas and
alcohol.

Discovery of the fermentation process allowed early peoples to
produce foods by allowing live organisms to act on other ingredients. But our
ancestors also found that, by manipulating the conditions under which the
fermentation took place, they could improve both the quality and the yield of
the ingredients themselves.

Fermentation is one of the oldest ways humans have used microbes. Fermentation enhances the nutrient content of foods through the
biosynthesis of vitamins, essential amino acids and proteins, by improving
protein and fibre digestibility, by enhancing micronutrient bioavailability,
and by degrading antinutritional factors. It also provides a source of calories
when used in the conversion of substrates, unsuitable for human consumption, to
human foods.

Fermentation is carried out by
both bacteria (prokaryotes) and fungi (eukaryotes) during their metabolism. Both groups of organisms also
figure in the world of human disease, as they are both sources of antibiotics, as we'll see throughout this
module. Fermentation results in a number of byproducts that have many different
uses. As mentioned, the most well-known product of fermentation is ethyl
alcohol. This substance is both a beverage as well as a starter molecule for synthesizing other compounds. Since
fermentation is carried out in the absence of oxygen, we call it an anaerobic
process. It is a method by which organisms such as yeast obtain their energy by
converting sugars into other chemical compounds, particularly carbon dioxide
and water. Interestingly, our bodies also use this same anaerobic fermentation
to obtain energy from sugars when oxygen is in low supply in our blood, such as
during vigorous exercise. The products of this process are lactic acid and
water rather than the carbon dioxide and water that human metabolism normally
produces. In this day and age, pharmaceutical companies utilize the
fermentation carried out by microorganisms to produce antibiotics, hormones,
and specialized proteins such as antibodies and insulin (Fermentation processes enhance food safety by reducing toxic
compounds such as aflatoxins and cyanogens, and producing antimicrobial factors
such lactic acid, bacteriocins, carbon dioxide, hydrogen peroxide and ethanol
which facilitate inhibition or elimination of food-borne pathogens). This wide range of products is possible
because the bacterium or fungus involved in fermentation has been genetically
changed to produce a specific substance. Therapeutic properties of
fermented foods have also been reported.

In addition to its nutritive, safety and preservative effects,
fermentation enriches the diet through production of a diversity of flavors,
textures and aromas. It improves the shelf-life of foods while reducing energy
consumption required for their preparation. The production of fermented foods
is also important in adding value to agricultural raw materials, thus providing
income and generating employment.

Traditional fermentation processing is generally a spontaneous,
non-aseptic operations which result from the competitive activities of a
variety of microorganisms. In a bioreactor - which may consist of clay or metal pots, a basket, or a
simply hole in the ground lined with leaves - strains best adapted, and with
the highest growth rates, dominate under uncontrolled conditions. Optimization of process
controls and of the microbial flora associated with fermentations therefore
poses one of the biggest challenges in improving food fermentation technologies. Appropriate
quality control methodologies - e.g. use of high quality raw materials, proper
hygienic standards in the processing environment, proper packaging - also need to be
developed.

Improvements in process control through the development of more
appropriate bioreactors, particularly those suitable for solid substrate
fermentations, could improve the quality and quantity of fermented foods
available in developing countries. The selection and development of more
productive microbial strains, and the control and manipulation of culture
conditions could also increase the efficiency of fermentation processes.

Although the final step of fermentation (conversion of pyruvate to
fermentation end-products) does not produce energy, it is critical for an
anaerobic cell since it regenerates nicotinamide adenine dinucleotide (NAD+),
which is required for glycolysis. This is important for normal cellular
function, as glycolysis is the only source of ATP in anaerobic conditions.

Fermentation products contain chemical energy (they are not fully
oxidised) but are considered waste products since they cannot be metabolised
further without the use of oxygen (or other more highly-oxidised electron
acceptors). A consequense is that the production of ATP by fermentation is less
efficient than oxidative phosphorylation, where pyruvate is fully oxidised to
carbon dioxide. Fermentation produces two ATP molecules per molecule of glucose
compared to approximately 36 by aerobic respiration. Even in vertebrates,
however, it is used as an effective means of energy production during short,
intense periods of exertion, where the transport of oxygen to the muscles is
insufficient to maintain aerobic metabolism. In humans, for example, lactic
acid fermentation provides energy for a period ranging from 30 seconds to 2
minutes. The speed at which ATP is produced is about 100 times that of oxidative phosphorylation. The pH in the cytoplasm
quickly drops when lactic acid accumulates in the muscle, eventually
inhibiting enzymes involved in glycolysis.

The fermentation process is caused by enzymes, catalysts in
chemical reactions similar to the digestive enzymes in the human body. Certain
enzymes act on starch to break down the long chain-like molecules into smaller
units of sugar. Then other enzymes convert one kind of sugar molecule to
another. Still other enzyme reactions break apart the sugar molecule (composed
of carbon, hydrogen and oxygen) into ethyl alcohol and carbon dioxide gas.The production of carbon dioxide and alcohol are incidental
to the release of energy needed by organisms such as yeast to survive. But
these metabolic by-products have been used in human enterprise for centuries.
The yeast Saccharomyces cerevisiae is traditionally added to liquids
derived from grains and fruits to brew beer and wine. The natural starches and
sugars provide food for the yeast and during fermentation the desired alcohol
is released. In China
for thousands of years, traditional soy sauce or shoyu was brewed by adding the
fungus Aspergillus oryzae to a mixture of boiled soybeans and wheat and
allowing it to ferment for about a year.In recent times, yeasts have been used to aid in the
production of alternative energy sources. Yeasts are placed in large
fermentation vats containing organic material. During fermentation the yeast
convert the organic material into ethanol fuel. Researchers are working on
developing yeast strains that will convert even larger organic biomasses into
ethanol more efficiently.

Products

Products produced by fermentation are actually waste products
produced during the reduction of pyruvate to regenerate NAD+ in the absence
oxygen.

Ethanol fermentation (done by yeast and some
types of bacteria)
breaks the pyruvate down into ethanol and
carbon dioxide. It is important in bread-making, brewing, and
wine-making.
When the ferment has a high concentration of pectin, minute
quantities of methanol can be produced. Usually only one of the
products is desired; in bread the alcohol is baked out, and in alcohol
production the carbon dioxide is released into the atmosphere.

The burning sensation in muscles during hard exercise used to be
attributed to the production of lactic acid
during a shift to anaerobic glycolosis, as oxygen is converted to carbon
dioxide by aerobic glycolysis faster than the body can
replenish it; but muscle soreness and stiffness after hard exercise is actually
due to microtrauma
of the muscle fibres. The body falls back on this
less-efficient but faster method of producing ATP under low-oxygen conditions.
This is thought to have been the primary means of energy production in earlier
organisms before oxygen was at high concentration in the atmosphere and thus would
represent a more ancient form of energy production in cells. The liver later gets rid
of this excess lactate by transforming it back into an important glycolysis
intermediate called pyruvate. Aerobic glycolysis is a method employed by
muscle cells for the production of lower-intensity energy over a longer period
of time.

Bacteria generally produce acids. Vinegar (acetic acid)
is the direct result of bacterial fermentation. In milk, the acid coagulates
the casein,
producing curds. In pickling, the acid preserves the food from pathogenic and
putrefactive bacteria.

Fermentation has some benefits exclusive to foods. Fermentation can
produce important nutrients or eliminate antinutrients. Food can be preserved by fermentation,
since fermentation uses up food energy and can make conditions unsuitable for
undesirable microorganisms. For example, in pickling the
acid produced by the dominant bacteria inhibit the growth of all other
microorganisms.